@ThomasWal @isi 

Hello, to help locate this issue, we need the information below:

1. The led status of TL-WPA4220kit when you lost connection.

2. The IP address and gateway obtained by your computer/cellphone which connects to the TL-WPA4220 when it stops working.

3. Have you ever verified the wired connection of the TL-WPA4220 at the same time? Does it work?

4. What about the main router? Try to connect your computer to it directly to confirm it.

5. You can use the tpPLC utility to disable the power saving mode and customize some wireless settings, like wireless channel and channel width. 

https://www.tp-link.com/support/faq/1611/ & https://www.tp-link.com/support/faq/2018/

6. Besides, please ensure that the current firmware is up to date. 

May it help.